1. Field of the Invention
The present invention relates to a portable telephone set, and more particularly to a technique of rewriting part of program data of a main memory of a portable telephone set to correct bugs of software.
2. Description of the Related Art
In recent years, the number of subscribers of portable telephone sets has increased and is increasing suddenly, and also the manufactured number of portable telephone sets has been and is increasing similarly. Portable telephone sets not only have mere telephone functions but also begin to have functions as an information terminal. In order to implement functions as an information terminal, development not only of hardware but also of software has significant weight. From such significance of software, a bug upon shipment of portable telephone sets in most cases gives a critical blow to sales of the portable telephone sets.
Conventionally, if a bug of software occurs with a portable telephone set, then when the bug is found out and therefore the software must be corrected, data must be rewritten over the entire area of a memory (ROM) of the portable telephone set from a descriptive configuration of the software. Accordingly, in order to rewrite the software for portable telephone sets that have been placed on the market once, a countermeasure of voluntary recovery by the maker is taken. However, much time and labor are required for such voluntary recovery. Therefore, it is demanded to provide a portable telephone set whose software can be rewritten by a user in order to eliminate such voluntary recovery.